extending Python - passing nested lists

[Christian Meesters]

Hi,

I would like to write a C-extension function for an application of mine. For
this I need to pass a nested list (like: [[a, b, c], [d, e, f], ...], where
all letters are floats) to the C-function. Now, with the code I have the
compiler is complaining: "subscripted value is neither array nor pointer".
Can somebody tell me what's wrong?

Here a code snippet to reproduce this problem:

static PyObject *_foo(PyObject *self, PyObject *args) {
  int i;
  long lenght;
  float ax, ay, az;
  PyObject *dummy_list;
  
  if (!PyArg_ParseTuple(args, "O", &dummy_list))
    return NULL;
  dummy_list = PySequence_Fast(dummy_list, "argument must be iterable");
  
  lenght = PyObject_Length(dummy_list);
  
  for (i=0; i < lenght; i++) {
    // part which does not work:
    ax = dummy_list[i][0];
    ay = dummy_list[i][1];
    az = dummy_list[i][2];
  }
  return 0;
}

TIA
Christian